1. Field of the Invention
The present invention relates to a technique that automatically adjusts operating characteristics of an image display apparatus.
2. Description of the Related Art
Liquid crystal panels and DMDs™ (digital micro-mirror devices: trademark by TI Inc.), spatial light modulators, are widely used as image display devices in projectors. Liquid crystal panels and PDPs (plasma display panels) are also widely used as direct view image display devices.
An image processing device included in an image display apparatus with such a display device digitizes input analog image signals and makes the digital image signals subjected to various series of image processing. Images expressed by the image signals output from the image processing device are displayed on the display device. The image processing device has diverse electronic circuits including an A-D converter to digitize the input analog image signals.
The image processing apparatus includes analog devices, such as a switch for selecting image signals, a video amplifier, and an A-D converter. The difference in damping characteristic of the image signal among these analog devices or the difference in damping characteristic among RGB color signals causes a variation in luminance characteristic. The variation deteriorates the linearity of the luminance characteristic and the color reproducibility. The deterioration may worsen the quality of the display characteristics. In order to ensure the constant display characteristics, one proposed technique inputs a reference image signal as an analog image signal into each image display apparatus and carries out adjustment to ensure the optimum A-D conversion characteristics set in the A-D converter and the optimum display characteristics set in the display device at the time of assembly of the image display apparatus.
Among the operating characteristics of the image display apparatus, the A-D conversion characteristics of the A-D converter and the display characteristics of the display device, however, often vary with time and especially by aging. Adjustment at only the time of assembly may thus be insufficient. The operating characteristics of the image display apparatus also vary with seasons or with the working environments. Such variations may also make the initial adjustment insufficient.
It is thus highly demanded to make the operating characteristics of the image display apparatus readily adjustable even after shipment, as well as at the time of assembly of the image display apparatus.